Intracellular retention of hepatitis B virus surface protein mutants devoid of amino-terminal pre-S1 sequences

To study the mechanism of L protein-mediated, intracellular (pre-Golgi) retention of hepatitis B virus (HBV) surface proteins, a collection of HBV preS-S open reading frame variants bearing wild-type or modified preS extensions was expressed in human cells. When the secretion phenotype of the corresponding proteins was analysed, all surface proteins with rearranged preS domains were found to be at least partially retained. This held true, in particular, for two variant proteins lacking preS1 amino acids 1 to 19 (ayw), the preS1 myristylated N terminus and a putative retention domain, and for another variant lacking the entire preS1 domain plus the N-terminal portion (amino acids 1 to 12) of the preS2 domain. All the retained variants underwent intracellular dimerization/oligomerization via disulphide bonds to a degree comparable to that observed in well exported natural proteins. Our results show that retention can take place in the absence of L N-terminal sequences and does not imply inhibition of covalent oligomerization.